rob_bell

Well-Known Member

• Nov 28, 2016

• #21

Thanks Joe - I took the clock apart again, cleaned everything with contact cleaner. Good contacts with the circuit tester on my multimeter. The carbon contacts in the rubber buttons have a high resistance, but I don't know that this should be?



Either way, I connected it back up and still no time changing action from the buttons.

I ran out of time over the weekend to try "shorting" the pads with copper wire, but I shall give this a go. But if you have a PCB and rubber/carbon buttons going spare Joe, that'd be great!

 

rob_bell

Well-Known Member

• Jan 1, 2017

• #22

I'm really stumped by this clock. I've checked the contacts and the circuit continuity on the pcb, and everything seems to check out. But I still can change the hour or minute. Frustrating.

Reads the right time now as the clock defaults to 1:00 and I plugged it back in at 1pm!

Here's the pcb in case you guys can spot something I didn't

 

Nodge68

Well-Known Member

• Jan 1, 2017

• #23

The picture isn't clear enough to trace all the tracks accurately. However both buttons are fed from a common track. There's a resistor in that track marked R1. It's legend shows 203 which is 20,000 ohms, or more commonly 20K. It's worth putting a DMM across each end to measure it's resistance, just to check it is still actually 20K. From there onwards, I can't see where the track goes.

 

davidsmith1307

Well-Known Member

• Jan 1, 2017

• #24

Putting a DMM across a resistor in-circuit won't necessarily tell you its resistance - depends what else is effectively in parallel.

 

Nodge68

Well-Known Member

• Jan 1, 2017

• #25

davidsmith1307 said:

Putting a DMM across a resistor in-circuit won't necessarily tell you its resistance - depends what else is effectively in parallel.

Click to expand...

True. It doesn't look like anything in parallel in this instance. The switch contacts just pull high or low. I can't tell without looking at the circuit. The 20K is only there to reduce current flow to a few micro amps.

 

NeedleNose

Active Member

• Jan 1, 2017

• #26

I see you've cleaned the rubber button pads, but you could try rubbing a soft pencil over the pads to (temporarily) restore the carbon. It's a cheap thing to try.

 

rob_bell

Well-Known Member

• Jan 2, 2017

• #27

Thanks guys. I've measured the resistance over that surface mount resistor. On my multimeter, it reads 16k rather than 20k, but whether that's an accurate reading I'm not sure. The other resistors (on other circuit tracks) read appropriately.

I've tried shorting the contact pads with copper wire with the clock powered: still no difference - the hour and minutes remain stubbornly unadjustable.

The common track runs to the loom connector - which picks up on the light green/ white cable. I've not yet looked up the RAVE wiring diagram to see where that goes?

 

Last edited: Jan 2, 2017